Pretty much any modern OS supports SCTP. HTTP wasn't built off it because HTTP came long before SCTP, but you won't find many protocols built off SCTP anyway, b

Pretty much any modern OS supports SCTP. HTTP wasn't built off it because HTTP came long before SCTP, but you won't find many protocols built off SCTP anyway, because it's poorly supported by middle-boxes and firewalls. Just look at any cloud firewall for example, you can open TCP or UDP, but not SCP or any of the "lesser known" protocols. It's currently in an unfortunate chicken and egg problem, where crappy firewalls don't support it because it's rarely used, and it's rarely used because crappy firewalls don't support it, but are everywhere on the public internet. HTTP3 actually does propose changing the transport protocol, but to QUIC, which is a transport over UDP.